Visible light responsive Zeolite/WO3–Pt hybrid photocatalysts for degradation of pollutants in air

Abstract

Adsorbent–photocatalyst hybrids based on WO3 and Pt as cocatalyst immobilized on different type of zeolites were prepared. Their performance for the degradation of pollutants under UV and Vis light was analyzed. Two types of zeolites (ZSM-5 and Zeolite Y) with Si/Al ratios ranging between 5 and 280 were selected as hierarchical microporous materials acting as adsorbents. The incorporation of platinum on tungsten oxide was done by means of the photodeposition method. Pt-loaded WO3 was dispersed on the zeolites and subjected to a lyophilization process. Their photocatalytic properties towards the abatement of representative pollutants e.g., acetic acid, acetaldehyde and trichloroethylene, were analyzed under different operating conditions in batch and continuous flow photoreactors. Raw materials and hybrid photocatalysts were characterized by N2 adsorption–desorption, XRD, UV–vis spectroscopy, XPS and TEM microscopy. The adsorption ability of the photocatalysts towards the selected pollutants was studied under dynamic conditions. The textural properties of the photocatalysts were not the main factor controlling their adsorption ability. The incorporation of WO3–Pt on the zeolite results in Vis light responsive materials. Monoclinic WO3 crystal phase was identify in all zeolitic materials. Large WO3–Pt aggregates were detected on Zeolite Y (ca. 300nm) with low Si/Al content in contrast with highly disperse phase for ZSM-5 (SiO2/Al2O3=280) (ca. 100nm). All WO3–Pt hybridized zeolites showed photoactivity for the degradation of the studied pollutants under Vis light, improving the performance of bare WO3–Pt. The results shown in this work reveal the influence of the hydrophobicity of the siliceous material for the adsorption of reaction intermediates or byproducts and as a consequence for the determination of the rates of CO2 formation under static conditions. A F(Static) function, dependent of the Si/Al ratio and the BET area, to correlate the difference trend of the amount of CO2 released produced by the hybrid composites, under static and dynamic conditions is proposed.